Rod guides formed or installed on sucker rods in secondary recovery efforts have been used for some time to center the sucker rod within a hole. The sucker rod must extend from a pumping unit all the way down to the reciprocating pump, which may be several thousand feet below the surface. Consequently, the sucker rod is subjected to a variety of stresses: compression, tension, torsion, and bending. Further, the sucker rod can "wobble" or bend within production tubing. This problem of "wobble" or bending has been solved by the installation of rod guides on the sucker rod to centralize the sucker rod within the production tubing thereby controlling rod and tubing wear.
A prior art sucker rod guide includes a body that is molded in intimate contact with the sucker rod. The body has simultaneously molded therewith a plurality of "fins", "blades", or "vanes" that extend radially from the body. As used herein, the terms "fin", "blade", and "vane" refer to the molded portion of the rod guide that extends from the body to guidingly contact the interior surface of production tubing.
As the rod guide is used within the production tubing, the outer extremities of the guide vanes wear away. The total volume of rod guide material that is available for wear (before a coupling is subjected to contact with the interior surface of production tubing) is known as "erodable volume." In one sense, all other factors being equal, the greater the erodable volume, the longer the useful lifetime of the rod guide. Once the vanes wear down to a point to where a coupling between rod guide segments contacts the production tubing, the rod guide must be replaced.
When a rod guide is replaced, the entire material remaining in the rod guide is disposed of, usually a majority of the material from which the rod guide was made. High performance polymers have been used in the past to provide the longest useful lifetime for the rod guide, while maintaining low coefficients of static and dynamic friction and sufficient resistance to failure in high pressure and velocity environments. Such high performance polymers are expensive and it is wasteful to dispose of the unused guide material. Thus, there remains a need for a rod guide in which the majority of rod guide material is not disposed of when the erodable volume has been expended.
Further, as previously described, the rod guide is customarily made of a body, molded in intimate contact with a rod segment, and integrally molded vanes protruding radially therefrom. The rod guide body serves only to secure the vanes which provide the erodable volume. Thus, the rod guide body is not subjected to the same forces and erosion as the vanes and need not be constructed of the same material to satisfy the same design criteria. Therefore, there remains a need for a rod guide in which the rod guide body is made of a commodity material while the vanes of the rod guide are made of a specially formulated material that maximizes erodable volume performance. Further, the rod guide body should be reusable by simply replacing spent vanes. Such a rod guide body should be adaptable to a variety of tubing sizes by simply changing to a vane height specifically designed for a particular tubing application.